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DIY: Summer Projects

Silou

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Are you planning to mount the volpot on the board or via (short) wires to the board ?
With wires. I was looking at some tiny potentiometer PCBs to make it a bit easier.

Low Gain Ratio = 1 + R16/R17
High Gain Ratio = 1 + R16/R19

So 1X gain is usually achieved by leaving out the gain resistors. If R16=1500 than R17 should theoretically have a very high resistance (1,0 mOhm?) and R19=750. Am I wrong?
 
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solderdude

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With 1x gain you won't be able to reach max output voltage.

For 1x gain indeed simply leave out R17 and R21.

As you plan to use the tone board which has 2.0Vrms output voltage the max output voltage = +/- 2.8V.
To ensure there is no clipping yet max output voltage can be reached I recommend to set at least the high gain setting to 3.3x (680 Ohms) but 750 Ohm can also be used and is on the safer side.
 

solderdude

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Only 680 or 750 will do I suppose.
 

Silou

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They are all rated at 0.6W or 0.25W is that fine?

The LEDs and the power switch LED need direct current. How do I power the LEDs without using a second power supply? I could probably use the Tone Board for that, but I do not plan to put it in the same chassis as the amplifier. Maybe I should install the batteries on one board and power the LEDs with them?
 
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solderdude

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yep, any rating in that area is fine.

You power the LED's through a resistor.
The required value will depend on the indicator itself, power supply voltage, color and how bright you want it.
Can be any value between a few kOhm and 100kOhm (for 12V supply voltage).
Indicator LEDs draw a few mA at the most so can safely be drawn from the V+ 12V supply voltage.
 

Silou

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I have just measured all resistasnces and sorted everything by values. Seems like everything is fine and nothing is missing.

Can you recommend a good solder for these small parts? I only have 1,5mm and 1,0mm solder at home but I am afraid they are too thick. Conrad does not sell 60/40 solder to private customers anymore :confused:
 
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solderdude

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1mm solder should be fine.
I use 0.7mm in general but also have 1.0mm.

Found THIS
 

Silou

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The 1mm solder is SN99,3 and CU0,7 though. I might get a good one from my unlce today. Let´s see.
HD58X Filter is finally done. Does not look as good as the other ones, but there was no other way to solder both parts together.
My uncle gave me a lot of 1,0mm 60/40 solder and a nice PCB holder :)
IMG_20190811_133221.jpg
 
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Silou

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So what do I need to modify the negative board besides the 2.2k resistors and the 100pF capacitors?
 

solderdude

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negative side.jpg


C19, C20 = 100pF
R16, R17, R21, R22 = 2k2
R14, R20 = 100 Ohm
 

solderdude

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The V+, GND and V- from C8 and C9 of the + side board will going to be connected to V+, GND and V- from C8 and C9 of the - side board

pin 1 (Left side R17) from the - board will be connected to pin 1 of U4A (left side R18) of the + side board.
pin 4 (Left side R21) from the - board will be connected to pin 1 of U#A (left side R11) of the + side board.

Pin 3 and 4 of the P2offboard connector of the - board will have the output signals for the - sides of the XLR's (these do not go through the filter switch)
 

Silou

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C19, C20 = 100pF
R16, R17, R21, R22 = 2k2
R14, R20 = 100 Ohm
Do these numbers also apply to the positive board?
I already soldered R14 and R20 10k Ohm before I thought about it.

I just realized that all the diodes are missing :confused:
 
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solderdude

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only the negative board.
The positive board is standard O2 minus some earlier mentioned parts (diodes 1N5818) and R1, R2.

Only D3 and D4 (1N400x) and D7 (LED) are needed for the + board.
 

Silou

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How do I know which opamp socket is the correct one and what is the correct orientation?
I have got:
1x S8
1x O8
2x A8 (probably U3 & U4)
 

solderdude

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Isually there is a notch in the socket indicating between pin1 and pin8
All opamps are DIP8.
They should either have a notch between 1 and 8 or have a dot near pin1
Pin 1 is the square pad on the PCB

I recommend the so-called 'turned pin' sockets over the cheaper spring loaded ones.
 

Silou

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I populated the positive board today. I am not sure if the solder joints are ok though. Some look not that clean, but it is far worse on the photo than in reality. Do I have to be worried about the burnt places?
D3, D4 ,all the mosfets and the gain resistors are still missing.
IMG_20190812_162456.jpg

IMG_20190812_162546.jpg
 

solderdude

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trry removing the flux residu (the balck stuff ?) with some alcohol and an old toothbrush.

Look at the solderjoints with a magnifying glass and simply reflow and add a little solder at the same time.

To solder any parts: put the tip of the solder iron to the pad and pin and add some solder to it.
Flowing the solder should be possible in 2 seconds or so.
 

Silou

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trry removing the flux residu (the balck stuff ?) with some alcohol and an old toothbrush.

Look at the solderjoints with a magnifying glass and simply reflow and add a little solder at the same time.

To solder any parts: put the tip of the solder iron to the pad and pin and add some solder to it.
Flowing the solder should be possible in 2 seconds or so.
I thought I burnt the PCB by holding the soldering iron to long to the pin. If that is only flux residu it is fine. I did it like you described it and it worked great most of the time. I hope that is what you meant, regarding D1 and D5.
IMG_20190812_164917.jpg
 

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